Experimental investigation on the secondary motion downstream a pipe bend with and without swirl

Authors: Kalpakli Vester, A., Örlü, R.
Document Type: Conference
Pubstate: Published
Journal: Proc 9th Int. ERCOFTAC Symposium on Engineering Turbulence Modeling and Measurements (ETMM9), Thessaloniki, Greece, Jun. 6-8 (2012)
Volume:    1-6
Year: 2012


The turbulent swirling flow at the exit of a 90 degree pipe bend, generated through an axially rotating pipe upstream the bend, is investigated by means of time-resolved stereoscopic particle image velocimetry. In particular, the behavior of the Dean vortices under turbulent flow conditions, the so called “swirl switching”, has been visualized with the aid of proper orthogonal decomposition. This phenomenon could be reconstructed by only a few of the most energetic modes. With the increase of the swirl number, defined as the azimuthal velocity of the rotating pipe upstream the pipe bend to the bulk velocity, the two Dean cells tend to merge for a swirl number close to unity. Vortical cells, similar to the Dean vortices, are found beneath the primary swirling motion, and are captured in the first mode of the decomposed field. The present investigation constitutes–to the authors’ knowledge–the first experimental study of the three velocity components in a swirling turbulent pipe flow across the exit of a pipe bend.